This invention relates generally to fluid operated machine controllers for loaders and, more, particularly, to a method for automatically controlling actuator operation to minimize frame stresses.
Various systems for controlling the operation of the lift actuators (e.g., lift cylinders) of a wheel loader or a backhoe loader are known. Typically, the controller enables a vehicle operator to control the lift of a working implement (e.g., a bucket) by way of a fluid operated system. The fluid operated system normally includes a pair of actuators, one of which acts upon each side of a frame to which the working implement is attached. The two actuators must be operated uniformly with respect to each other to avoid conditions such as the application of uneven forces to the frame, which can cause twisting or other structural damage to the frame. If these forces are sufficiently imbalanced, permanent damage or a hazardous condition will result. This problem may also occur when one actuator has partially or completely failed. In this circumstance, the failure of the actuator to function in the intended manner may not be detected until damage is done. One approach to controlling the operation of a plurality of actuators to produce uniform operation is to attempt to control the flow of fluid to each actuator so that this flow is approximately equal. This approach is flawed because it cannot compensate for a failed actuator, or an actuator which leaks fluid and hence requires that more fluid be delivered to produce the required operation.
Another method of assuring uniform operation involves the reinforcement of the frame structure by the addition of bracing and reinforcing mechanisms. This approach is also unsatisfactory because it adds significant weight to the frame structure, resulting in a decrease in the payload capability of the machine, and at the same time requiring upgrading of the frame control mechanisms so that these mechanisms can properly operate with the increased load. Thus, the expense of the vehicle is increased. At the same time, however, this approach does nothing to address problems resulting from malfunctions of the actuators. The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.
A first aspect of the present invention provides a controller for load manipulation of a device by a first actuator and a second actuator, said controller comprising: an input device for receiving a first displacement signal and a second displacement signal, said first displacement signal from a first displacement sensor, said first displacement sensor operationally attached to said first actuator, and said second displacement signal from a second displacement sensor, said second displacement sensor operationally attached to said second actuator; a comparator for comparing the first displacement signal and the second displacement signal to determine a maximum differential value; and an output device for providing a signal to adjust the first and second actuator to be within a predetermined range for the maximum differential value, thereby preventing damage to the device.
A second aspect of the present invention provides a control system comprising: at least two lift actuators; a control valve, operatively connected to each of said lift actuators; a displacement sensor, operatively connected to each of said actuators to determine the amount of travel of the pistons of said actuators; a controller for comparing outputs from the displacement sensors and for operating said control valves to adjust the amount of travel of said pistons in response to the outputs of the displacement sensors.
A third aspect of the present invention provides an earth working machine comprising: at least two lift actuators; a control valve, operatively connected to each of said lift actuators; a displacement sensor, operatively connected to each of said actuators to determine the amount of travel of the pistons of said actuators; a controller for comparing outputs from the displacement sensors and for operating said control valves to adjust the amount of travel of said pistons in response to the outputs of the displacement sensors.
A fourth aspect of the present invention provides a control method for an implement attached to a frame on an earth working machine with first and second fluid operated actuators being operatively connected to the frame, and first and second control valves being adapted to deliver pressurized fluid to the actuators, comprising the steps of: producing an implement move command signal in response to a position of a control lever; receiving the implement move command signal and responsively delivering an implement move control signal to the first and second valves to cause pressurized fluid flow to actuate the first and second actuators to move the implement; producing a first position signal indicative of the extension of the first actuator; producing a second position signal indicative of the extension of the second actuator; and receiving the first and second position signals, determining a magnitude of the difference between the relative positions of the first and second actuators, comparing the magnitude difference to a maximum differential value, and stopping the delivery of the implement move control signal in response to the magnitude difference being substantially equal to the maximum differential value, the maximum differential value representing the maximum imbalance that the frame can withstand without damage.
A fifth aspect of the present invention provides a method of controlling loader lift cylinders comprising: providing a machine control system operatively coupled to the lift cylinders, wherein the machine control system includes means for determining the amount of extension of each of the lift cylinders; comparing the amount of extension of each lift cylinder; and adjusting the amount of extension of each lift cylinder in response to the amount of extension that is detected.
The foregoing and other features and advantages of the invention will be apparent in the following more particular description of preferred embodiments of the invention.